Lightning Protection

[kelkara]

I have a ground plate laminated in my "fiberglass" hull (sorry for the wrong material)which was connedted to the upper s/s shrouds by a g8 insulated wire.
I would like to reroute it and attach it directly to the s/s bolts of the aluminium mast shoe to maintain a straight as possible path to the ground plate - as is suggested in the literature.
Could that cause increased electrolisys - so far there is none?
And if so, how can I make sure that there is an uninterrupted path to the ground plate?

[Ian McColgin]

Dirty Harry had a simile for what anatomical feature opinions most resemble but anyway:

The bonding of shrouds to the ground plate is intended, if whoever did it had a coherant theory, to make what amounts to a gauss cage and protect the interior of the boat.

You might also check what happens to the head stay and back stay. In real life, the back stay is thought to present a hazard, especially if you have an edson type steering system located near it, as a strike could (or is believed might) flash from the back stay down the rudder post, carmelizing the helmsman along the way.

On a boat with wooden masts, I've always been happy to have the shroud to groundplate connection be it. But with a good conductor mast like aluminum and just a short distance to the ground plate anyway, I'd recommend adding a strap from the heel of the mast or the step to the ground plate. I'd not remove the grounds from the chain plates. During a storm, try to keep crew away from between the shrouds and the mast when below.

G'luck

[paladin]

If struck by lightning....any wire that you use will probably vaporize.......and at the base of the mast..vaporize right through the bottom of the boat...wire is not a good "ground"...flat strap am more better...and to be technically accurate....the width of the ground strap should be NO LESS than 10% of the length...have you ever seen a 4/0 wire vaporize so fast that the insulation didn't burn through?

[Dave Hadfield]

Or you can just forget about it and anchor next to the sloop with the really tall aluminum mast.

I know sailboats get struck from time to time, but it seems, considering the numbers, to be pretty rare.

My own opinion, for what it's worth (no technical knowledge here) after surviving countless mid-continent Cold-Front passages, is that the electric potentials involved are so huge, that for a sailboat to be "noticed" is like a horse considering a grasshopper.

It's the wind I worry about during thunderstorms.

[John Meachen]

I have witnessed one lightning strike at sea.It was in the mid 1980's and a cruising boat of almost forty feet with a metal mast had just come into sight on a changeable day for weather.A storm came in and after a while a fork of lightning hit the masthead electrics which disintegrated.From a selfish point of view,I'm relieved they were there as I was sitting very close to the next tallest mast in the vicinity.
A few years earlier,a friend had his wooden cruiser with a wooden mast sunk by lightning.The shroud was the conduit for the lightning and the chainplate finished only a few inches above the waterline.The discharge loosened the fastenings in the hull and the bulkhead at the aft end of the fore-cabin.The loosened planks allowed water in and the boat sank.Not as bad as it might have been as it was on a mooring with around six feet of water at most.When the boat was raised it was found that the mirror in the fore-cabin had shattered and thrown shards of glass around with considerable force.Happily,the incident occurred in midweek when the boat was empty.

[WindHawk]

I was cuaght on foot during an extreme lighting storm on Woodward Ave. in Royal Oak, Michigan in 1985. In fact, the kind soul who finally stopped & rescued me said he only stopped because he saw a leader jump from my head to the sky (I didn't feel a thing). He wanted to know if it hurt. This means that my one-in-10,000 chances were down to, at best, one-in-five, and more likely, one-in-three.

If you've never been outside, unprotected, when the strikes are occuring at the rate of 4 or 5 per minute (an astounding number), and they are all withing a one-mile or so radius of you, you cannot imagine the terror. All I could do was press my body against the only building within 200 yards. I didn't see any advatage to making a run across open ground to the next building, not knowing if there was any more protection to be found.

All of that, is a long way of saying that I don't think I'd trust lying a hull in the shadow of a larger boat. To my mind, here in the midwest, and probably along the sourthern coasts as well, your only two choices are to get off the boat, or have an expertly installed ground system.

On the other hand, if you're struck, you won't feel a thing unless you're unlucky enough to live. That may be an OK risk to assume if you're a single-hander.

The argument can be made that grounding your boat presents a more inviting target, but that's getting rather hypothetical. It is odd that more deaths are caused on powerboats than sailboats. I've always chaulked up that last fact to the possibility that God hate's powerboats... ;)

[Jonas]

My understanding of why sailors on sailboats are safer than on powerboats is that the mast and shrouds divert the charge around the crew.

Would bonding the shrouds, mast, etc. to the lead keel work as well as to a dedicated grounding plate? How well does lead conduct electricity? How would one construct a grounding plate and where would you put it?

[paladin]

In free space the charge travels 186000 miles per second, or there abouts..it's sorta like dynamite, you cannot make a shaped charge because of the speed of the explosive so it goes in all directions simultaneously....
When lightning "goes to ground" at that speed it heats everything SUDDENLY.
Any bolt or thru hull that you fabricate will probably heat up around itself instantaneously and burn a hole in the hull.Probably (I would guess) the best thing is to attach a heavy wire to the chainplate and throw it over the side of the boat to dangle in the water.......

[mmd]

For those who are interested in the subject of lightning protection for their boats, I'd strongly reccommend that you contact our host's sister publication and order a back issue of Professional Boatbuilder No. 86 (Dec/Jan 2004). There is an extensive and excellent article by Nigel Calder on the subject. Mr. Calder also has written a book that discusses this (and other pertinent topics) entitled Boatowner's Mechanical and Electrical Manual. The second edition is current, a third edition is imminent.

[ahp]

An aquaintance of mine, an electrical engineer, had his own inexpensive lightening protection. His was a 20 ft fiberglass sailboat with an aluminum mast. He had four, six foot lengths of chain (size ?) with snapshackles on one end. He would attach these to the forestay, backstay and the shrouds, and let the other end dangle in the water.

I don't know how effective it was. He was never hit.

[kc8pql]

Here's a site maintained by a professor of electrial engineering at the University Of Florida. It's the most complete treatment of lightning and boats I've seen. Lightning Protection (http://www.thomson.ece.ufl.edu/lightning/)

[ 11-02-2004, 07:17 PM: Message edited by: kc8pql ]

[WindHawk]

That's a great site. They say that grounding the boat does not increase the chances of a strike.

Also, "Tragedies occur on both sailboats and power boats, but lightning kills or injures more people on open boats because it is more likely to strike crewmembers when there is no mast. "

I guess that dispels the notion the God hates power boaters, and puts the blame on people too silly to put a mast on their boat. :D